Need help For which starting number will this calculation program not be able to give a result? Why?

program:
- when flag is pressed
- ask for starting number and wait.
- put number to answer
-add to number -3
-set number to 1 / number.
-add to number -2
- say number for 2 seconds.​

Use the frequency distribution, which shows the number of american voters (in millions) according to age, to find the probability that a voter chosen at random is in the 18 to 20 years old age range. ages frequency 18 to 20 5.9 21 to 24 7.7 25 to 34 20.4 35 to 44 25.1 45 to 64 54.4 65 and over 27.7 the probability that a voter chosen at random is in the 18 to 20 years old age range is nothing. (round to three decimal places as needed.)

What is the missing step in this proof ?

Aquadratic equation in standard from is written ax^2= bx+c, where a,b and c are real numbers and a is not zero?